1. Technical Field
The disclosure relates to a position detection system for detecting a position of a capsule medical device introduced into a subject.
2. Related Art
In the related art, there has been developed a capsule medical device which is introduced into a subject to acquire various types of information on internal portions of the subject or to administer drugs into the subject. As an example, in the field of endoscope, there is known a capsule endoscope having a size enough to be introduced into the gastrointestinal tract (lumen) of a subject. The capsule endoscope has an imaging function and a wireless communication function inside a capsule-shaped casing, and after being swallowed into the subject, the capsule endoscope performs imaging while moving along the gastrointestinal tract by peristaltic movement or the like and sequentially transmits images (hereinafter, referred to as in-vivo images) of organs of the subject wirelessly. The wirelessly transmitted image data is received by a receiving device provided outside the subject and is further received into an image processing device such as a workstation, where a predetermined image process is performed. Therefore, in the image processing device, an in-vivo image of the subject is reproduced and displayed as a still image or a moving image.
In order to identify a portion of the subject in such an in-vivo image, a position detection system for detecting a position or posture of a capsule medical device in the subject has been developed (See International Publication Pamphlet No. WO 2007/064013 and Japanese Patent Application Laid-open No. 2008-275395). For example, WO 2007/064013 discloses a technique where a coil (marker coil) for generating an alternate-current (AC) magnetic field is provided in a capsule medical device, the AC magnetic field generated by the marker coil is detected by a plurality of coils (hereinafter, referred to as sensing coils) provided outside a subject for detection of the magnetic field, and a position of the capsule medical device is estimated based on a strength of the detected AC magnetic field.
However, in order to improve the accuracy of detection of the capsule medical device in the position detection system, incident direction of the AC magnetic field incident on the sensing coil, that is, the polarity of the sensing coil needs to be determined. In the related art, the magnetic field is detected by the sensing coil in synchronization with the generation of the magnetic field from the marker coil, and the polarity determination is performed based on the phase difference between the generated magnetic field and the detected magnetic field. For example, if the generated magnetic field and the detected magnetic field are in phase, the polarity is determined to be plus; and if the generated magnetic field is out of phase with the detected magnetic field by n) (180°, the polarity is determined to be minus.